Dyeing leather



Patented Feb. 9, 1937 UNITED STATES PATENT oF ics George B. Pensel, Amsterdam, N. v.

No Drawing. Application March 23, 1933, Serial No. 662,383

llClaims.

This invention relatesto the dyeing of leather and more particularly to processes and compositions which are well adapted for use in dyeing fine leathers, such as are employed'in the manufacture of gloves or shoe uppers.

The general object of. the invention is to provide certain novel and improved dyeing methods and compositions of the type described.

Other and more specific objects of my invention involve the provision of novel steps to be pursued in the pretreatment of tanned leathers which are to be colored, and also in the later stages of the process wherein the dye or coloring is set so as to render it fixed or to prevent bleeding". These objects also include the provision of novel compositions of matter which are adapted to be employed in these steps. These processes and compositions employed therein are especially applicable to the treatment of leathers which are to be colored upon one side only, the opposite side remaining in the white or original undyed condition, the dye being applied either to the grain or to the suede side and fixed or set before it has time to penetrate into the skin. The present invention is, however, not to be considered as so limited, but may obviously be embodied in processes in which leather is dyed on both sides.

Briefly considered, the present invention in its preferred embodiment contemplates the treatment of the tanned leather with a solution of acid (preferably organic) in methanol for the purpose of preparing the surface of the skin so that it will properly receive and be wetted by a the dye liquor subsequently applied, but-penetration through the skin is prevented. The invention also contemplates the after treatment of the dyed leather with a similar organic acid sov lution for the purpose of more completely setting the dye. In certain cases these treatments may be varied by the substitution, in either or both steps, of another novel compound containing basic chromium sulphate and cream of tartar for the organic acid solution. I

Other objects and features of novelty will be apparent to one skilled in the art from the following'specification in which certain processes and compositions embodying the principles of my invention are disclosed in considerable detall by way of example.

The leather, which has already been tanned by a suitable process such as by the use of formaldehyde or chrome tannage, is fat liquored by any well-known means and is put in a socalled crusted" state. This involves hanging up the skins to dry, subsequently dampening them and putting them on a staking machine, whereby the fibers are stretched and loosened in a damp condition. They are then "wet on in a drum with ordinary wetting out agents such as soap, sulinsoluble residues.

phonated oils or the like. me skins are then ready for brush dyeing. 7 They are placed individually upon a table having a spherical upper surface which allows the liquors todrain off the edges. The liquid is then squeezed out of the skins byslicking or scraping the leather with a piece of hard rubber of the 7 dimensions of about 8" 4" The skins are then treated with a solution of any of the following named organic acids in methanol: formic, acetic, lactic, oxalic, citric, tartaric, maleic and malic; the inorganic phosphoric acid may also be employed in this connection as well as numerous other organic acids of like properties. In practice, formic acid has been found to be as eflective as any. and anywhere from a 1% to a 10% solution has been employed depending upon the nature of the coloring to be applied. This acid solution is first brushed or sprayed on the skins in suitable amounts, usually a pint to a skin, after the water has been scraped out as well as possible with the slicker as already described. The water is therefore partially replaced with an acid solution of methanol. The excess of this acid solution is.

.At this stage, the surface of the skin which is to be dyed is thus not only prepared to be wetted by the spirit soluble color, but also contains a quantity of a fastening or setting composition which serves to liberate the color acid from the subsequently applied aniline dye in order to increase the aflinity of the color for the fibers. This has the eflect of setting or localizing the dyeing treatment sufiiciently near the surfam to which it is applied and to preventpenetration to the opposite or inner surface; thus preserving the original whiteness of the latter surface, which is highly desirable in preparing fine glove leather. g

Y The dye solution used may be a spirit soluble color selected from the well known aniline dyes. These solutions are usually made up by boiling the dyeewith methanol and then filtering off the The dye solution is cooled before being applied, is brushed or sprayed on the skin, and the excess removed by the use of the slicker as previously described. Additional coats of the same dye may be applied in the same manner.

After'the final slicking of the dye solution, the dyed skins are finally fixed by means of brushing or spraying on the skins a cold 10% aqueous solution of basic chromium sulphate combined with cream of tartar. This solution may be.

by the addition of cold water. A 10% solution is then made of this product. After the application of this solution, the skins are washed and ready for finishing. It has been found that the amount of basic chromium sulphate may be varied by a pound or so, and that the quantity of cream of'tartar may vary from pounds-up to the amount required to saturate the solution.

an alternative method of fixing, following the dyeing process, comprises applying the acid solution in methanol already described, over the first coat of dye, slicking out this solution and then applying another coat of dye. The methanolacid solution can also be used as a final fixing medium in place of the basic chomium sulphate and the cream of tartar solution.

In certain cases, for example in the brush or spray dyeing of black leathers, the chromium sulphate-cream of tartar solution may be used as a preliminary application in place of the methanol-acid solution. In all cases, however, the principle of the invention is the same, and the general purpose is served of ensuring the fixing of the dye upon the surface of the skin before it has a chance to penetrate or cause "bleeding" Among the advantages of the use of these solutions may be mentioned the effective fixation of the dye and also the preparation of the surface of the skin to receive the dyeing solution. Heretofore, it has been found impossible to brush or spray a skin through the fat liquor because of the surface tension of the water solutions employed. This difficulty has been entirely obviated by the use of my novel solutions.

It will be understood that the precise details of my novel process including the quantities and nature of the ingredients used may be varied without departing from the scope of the invention as defined in the following claims.

It is further understood that the application of the dye solution in the present process, when it is-to be applied to one side only of the skin, may be effected by brushing, sprinkling, spraying, or any equivalent process not involving the submersion of the entire skin in the solution. Generically, therefore, these methods may be referred to as surface application" or by a similar term.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. In a process of dyeing leather, in combination, the steps of applying an acid solution of methanol to leather which has been fat-liquored, removing the excess of said solution, applying the coloring material, removing the excess coloring material, applying an aqueous solution of basic chromium sulphate and cream of tartar, and then washing and finishing the leather.

,2.'In a process of dyeing leather, in combination, the steps of applying an acid solution of methanol to leather which has been fat-liquored,

applying the coloring material, fixing the latter upon the leather by theapplication of a solution of basic chromium sulphate and cream of tartar.

3. In aprocess of dyeing leather, in combination, the steps of applying to the leather which has been fat-liquored a solution of one or more of the following acids in methanol: acetic, citric, formic, lactic, maleic, malic, oxalic, phosphoric, and tartaric; dyeing the leather, and fixing the dye in the leather byapplying thereto an aqueous solution of basic chromium sulphate and cream of tartar.

4. In a process of dyeing leather, in combination, the steps of applying to the leather which has been fat-liquored a solution of 1% to 10% of one or more of the following acids in methanol: acetic, citric, formic. lactic, maleic, malic, oxalic, phosphoric, and tartaric; dyeing the leather, and fixing the dye in the leather by applying thereto a solution of the proportions of about 100 parts of basic chromium sulphate and from 20-40 parts of cream of tartar, and about 5000 parts of water.

5. In a process of treating leather, in combination, the steps of fat-liquoring the leather, crusting it and wetting it out, applying to the leather a solution of one or more of the following acids in methanol: acetic, citric, formic, lactic, maleic, malic, oxalic, phosphoric, and tartaric: removing the excess acid solution, applying one or more coatings of a dye solution, removing the excess dye solution, and fixing the color by the application of an aqueous solution of basic chromium sulphate and cream of tartar, washing and finishing the leather.

6. In a process for dyeing leather which has been tanned, the steps of fat liquoring the skins, slicking the skins to eliminate as much water as possible, applying to the skins a solution of formic acid in methanol as by brushing, spraying or the like, slicking oi! any excess solution, applying a suitable dye material also in methanol, slicking off the excess dye material, and then filing the color in the skins by applying a solution of basic chromium sulphate and cream of tartar.

7. In a process of dyeing leather on one side only, in combination, the steps of applying an acid solution of methanol to leather which has been fat-liquored, removing the excess of said solution, applying the coloring material to one side onLv oi the leather, removing the excess coloring material, applying of basic chromium sulplnte to the dyed side of the leather, ing and finishing the leather.

8. In a process of dyeing leather upon one side only of the skin, the steps of applying to the side oftheskinwhichistobedyedbyeurface application, a quantity of an accelerating and fastening agent, consisting of a methanol solution of an acid selected from the group consisting of formic, acetic, lactic, oxalic, citric, tartaric. maleic, phosphoric, and malic, then applying an aniline dye solution by surface application, whereupon the dye will be set through the skin to the opposite side which is to be maintained in an undyed condition, and then again applying a fixing sent for the dye employed to the dyed surface of the leather to let the excess dye.

9. In aprocess of dyeing leather upon one side onlyoftheskimthestcllsofap ylngtotheside of the skin which is to be dyed by surface application a quantity of an accelerating and fastening agent. consisting of imsthanol solution of an acid selected from the group consisting of formic, acetic, lactic, oxalic, citric, tartaric, maleic, phosphoric, and malic, then applying an aniline dye solution by surface application whereupon the dye will be set before it can penetrate through theskintothewpesitesidewhichis tobemaintainedinanundyedconditionand then effecting a further application of said acid methanol solution to the dyed surface of the leather to set the excess dye.

csoaosamm. 7

before it can penetrate 

